Process of manufacturing identifiable paper



Patented July 3, 1945 UNITED STATES PATENT OFFICE PROCESS OFMANUFACTURING I IDENTIFIABLE PAPER Morris S. Kantrowitz and Earl J.Gosnell,

Washington, D. C.

No Drawing: Application March 15, 1943,

Serial N0.-4794,186

(Granted under the act of March 3, 1883, as amended April 30, 1928; 3700. G. 757)- 2 Claims.

The invention described herein may be manufactured and used by or forthe Government of the United States for governmental purposes withoutthe payment to us of any royalty thereon, in accordance with theprovisions of the act of April 30. 1928 Ch. 460, 45 st. L. 467).

This invention relates to a process for manu- ,facturing indentifiablepaper, paper board or other cellulosic materials and to ameans for Ydistinguishing a portion of the cellulosic fibers thereof whereby theydevelop a distinctive color under chemical treatment, manipulationorreaction.

An object of this invention is the economic and efficient production ofpaper, paper boards and other cellulosic material which haveincorporated to counterfeiters.

therein cellulosic fibers chemically treated with inorganic chemicalsubstances, compounds, or materials. A further object of this inventionis the production of paper that may be used in Government bonds, legal.documentsypostage and revenue stamps, United States postal cards,

men under examination or test may have undergone considerable handlingin commerce even to the point of near deterioration.

'Identifiable'paper, as heretofore manufactured for use generally ascurrency or bank note paper had incorporated therein short red and bluesilk fibers as a means of identification. These silk fibers are visibleto the naked eye and are of origin foreign to the cellulosic fibers fromwhich the paper is fabricated. Identifiable paper has also been proposedwherein the mark of identification comprises fibers which arefluorescent under ultra violet light. We have found that byincorporating in paper a percentage of cellulosic fibers treated for thepurpose of identification with certain inorganic chemical substances,such as ferric chloride or the combination of ferric chloride andtri-sodium phosphate, advantages result which are not obtainable withpaper employing silk fibers or fluorescent fibers. One such advantage ofemploying fibers treated with inorgame substances, compoundsorqnaterials is that they are invisible within the paper structure tothe naked eye, and do not reveal their presence Another advantage ofemploying such fibers over the silk fibers is that they are preferablyidentical with the untreated fibers comprising the entire sheet ofpaper, and do not therefore involve increased expense for material andlabor.

Another advantage of employing fibers treated with inorganic chemicalsubstances, compounds 'or materials as compared with fluorescent fibersis that the invention is practical for use in the field, withoutexpensive ultra violet light equip-.

ment. The skill of a chemist or technician is not necessary, but alayman when properly instructed can detect the presence of the treatedcellulose fibers by means of certain inorganic chemical reagents whenapplied to a particular specimen of the paper, paperboard or othercellulosic material, which immediatelyrespond to such treatment byacquiring a colordistinctive from that of 'the untreated fibers and fromthat which they and the untreated fibers previously had. Anotheradvantage of the present invention is that unlike fluorescent fibers,the fibers treated with certain inorganic chemical substances,compounds, or materials cannot be destroyed in effectiveness, by'sunlight, bleaching agents, acids, alkalis, absorption of water, oil,gasoline, etc., and they therefore remain in the paper structure as apermanent means of identification.

The invention as herein described is particularly applicable to paper,this being a particular article of manufacture in which the utility ofsuch a device is especially desirable, and in connection with which theinvention has been tested on a production basis and found to besuccessful.

In accordance with our invention we form sheet cellulosic materials suchas tissue, manifold, writing, bond, ledger, index, paperboard or othertypes of material from any suitable cellulosic fibers and incorporate insaid cellulosic material a percentage of cellulosic fibers chemicallytreated with inorganic substances, compounds or materials of the sameorigin and production as the untreated fibers comprising the entirestructure of the sheet.

The base material of the paper or other cellulosic article ofmanufacture may be any suitable stock employed in the fabrication ofsuch cellulosic articles. For example, the paper or other .cellulosicarticle may be manufactured from chemical pulp produced by the suphite,sulphate, or soda process from wood or from any chemical pulpofvegetable or other origin. The paper or other cellulosic article may befabricated or formed on the same machines and in same man- Chemical woodpulp is disintegrated in the beater containing clear water held at atemperature preferably not exceeding 90 degrees Fahrenwith the untreatedpaper stock before the paper is made.

We have found that for the purpose of our invention the chemicallytreated fibers may be produced involving a combination of ferricchloride and tri-sodium phosphate. This method is completelysatisfactory and gives slightly different results which may be desiredin some instances.

- It can be carried out at either low or high pulp heit and kept at aconsistency of about 1.5 percent. The heater roll is heldin the raisedposition at all times, using it for circulation only. Commercial ferricchloride crystals also commonly known as 60 percent ferric chloridecrystals dissolved in warm water to give a substantially 30 percentsolution is added to the pulp suspension in the beater in amountconstituting about percent of the oven-dry weight of the pulp in thebeater. Steam is turned on and the temperature of the pulp mix is raisedto about 140 degrees Fahrenheit while the contents in the beater arecirculating. As the pulp heats up it gradually becomes brown in color.The circulation of the pulp is continued for approximately minutes atabout 140 degrees Fahrenheit after which about two percent rosin sizebased upon the oven dry weight of the pulp is added. The concentrationof the size solution when added to the contents in the beater must be 3percent or less. and it should preferably be added across the beaterjust in front of the beater roll. No alum is needed. The beater'contentsconsisting of the suspension of chemical wood pulp of about 1.5 percentconsistency and about 2 percent rosin size based on the oven dry weightof the pulp, are now circulated for at least 5 minutes or until suchtimeas it is considered that the rosin size has been well mixed into thepulp. The treated pulp suspension is diluted by filling the beater withcold water and the contents of the beater are circulated during theaddition of the water to provide thorough mixing. The contents of thebeater are dropped to a storage tank provided with a means for agitationaudit is further diluted in the tank to a final consistency of about 0.7percent. The

treated fibers in the agitated storage tank are kept at about 0.7percent consistency to permit accurate metering. The dilute stock ispumped continuously to a constant level over head stuff box and ismetered through an adjustable gate to a pipe which conveys it to themixing box of the paper machine. If a long pipe is used between gate andmixing box, additional dilution water may be introduced just after thegate to keep the treated stock flowing freely. The treated fibers areadded at the mixing box in order to avoid all beating and jordaningaction, which would shorten the fibers and might also loosen theadhering chemicals. Since a major requirement of this treated-fibermethod of paper identification is maximum length of treated fibers, theyare prepared without beating and they are added to the paper machineafter all refining action has been completed. An added feature of thelate point of addition is to provide as short a time as possible for thetreated fibers to be mixed concentration, but leads to a product inwhich there is no essential difference from that obtained with theferric chloride alone. It requires more labor and greater attention.However, if a mill for any reason is unable to heat the pulp undertreatment to the required temperature of about 140 degrees Fahrenheit,the use of tri-sodium phosphate might be necessary. In this instance itshould be added in 15 percent solution after the ferric chloride hasbeen heated with the pulp under treatment for 30 minutes with continualcirculation in the beater. The amount of crystalline trl-sodiumphosphate to use istwice the weight of the ferric chloride crystals.After the tri-sodium phosphate solution has mixed for about 10 minuteswith the stock, 2 percent rosin size based on the weight of oven-drypulp, at three percent concentration is added. The pulp is subsequentlyadjusted to pH 4.5 by the addition of alum. Any suitable percentage oftreated cellulose fibers may be mixed with the untreated cellulosicstock. For the purpose of our invention a suitable amount of treatedcellulose fibers is 0.8 percent based on the weight of the drycellulosic fiber comprising the finished paper. Obviously variations maybe made, smaller or greater percentages of the treated fibers may beemployed as desired.

As stated, this invention relates to the production of identifiablepaper or other cellulosic material that is to be used for any purposewhere identification is desirable or necessary and where theidentifiable characteristics or the distinguishing characters of thepaper or other cellulosic materials make possible the positivedetermination of their identity and authenticity or ready detection ofcounterfeit.

For an invention of this type to be of the desired practical value themethod of practicing it must be simple, reliable and economical. Thatis, it

- should be capable of being performed quickly remain for any desiredperiod during the marketwithout complication of apparatus or of expertchemical technique. It must be reliable-in the sense of giving resultswhich are constantly reproducible under ordinary industrial conditionsand under specifically prescribed procedure of examination or test.

This invention provides in the felted fabric of the finished paper orcompleted cellulosic product 'a percentage of permanent and invisiblecellulosic fibers which have been treated with a ferric or ferrouscompound alone, or in combination with a substance, such as a phosphatecarbonate or hydroxide, with which it will unite to give an insolublereaction product. Such treated fibers treated invisible cellulose fibersdo not affect the color, finish, formation, general appearance.

the feeling or other characteristics of the paper or cellulosic sheet inwhich they are incorporated and in which they are indistinguishable byphysical or ordinary non-chemicalomethods of inspection or test. Thefundamental principle in-this particular method and the chemicalmaterials involved as a means to establish the authenticity or identityof a particular specimen of the cellulosic product as here described, isthat the treated fibers do not possess the property of acquiring adistinctive color by emitting a fluorescence when exposed to ultraviolet light, but that the desired distinctive color of the individuallytreated fibers is produced by reaction of several chemical inorganiccompounds upon the chemically treated cellulosic fibers. It will thus beperceived that the invention by which the foregoing results are attainedconsists in the case of paper, paperboard or other cellulosicproducts'in providing chemically treated cellulosic fibers which reactdifferently from the way in which the untreated fibers that of thedispersed-cellulosic fibers, and'these I 1 components are thus attractedto each other, the

insoluble ferric hydroxide depositing on and within the cellulosicfibers. When the first component of the test solution, that is, when thepotassium ferrocyanide is applied to the specimen under examination ortest, at any particular time, days, months or even years after theproduction of the paper or cellulosic sheet, it does not impart color,nor does it produce any visible'change therein.

However, when the first component is followed by the second component ofthe test solution, namely,

react, when all are together subjected to an examination or testtreatment.

,In any instance or' at any time, days, months or even years after themanufacture of the paper or cellulosic material, or in any place howeverremote from'factory or laboratory the invisible treated fibers may bemade Visible by application of certain chemical inorganic compounds byacquiring a desired distinctive and permanent color.

The particular method for producing color by chemical reaction in theillustration here given for the purpose of this invention, is'the use ofpotassium ferrocyanide and orthophosphoric acid.

The potassium ferrocyanide employed isrecommended to be of reagentquality although cheaper grades of potassium ferrocyanide may serve as Iwell. For example, a sample of commercial or technical grade potassiumferrocyanide was found to be fully satisfactory for the purpose of thisinvention. The orthophosphoric acid employed is of a quality conformingto the specifications of the United States Pharmacopoeia now in effect.Other grades such as Chemically Pure or Technical Quality may also beutilized if their purity is first established by test.

A thin film of 20 percent aqueous solution of potassium ferrocyanide isapplied to the specimen of paper, paperboard or other cellulosicmaterial .under test or examination and then blotted to remove excessliquid. This treatment is then followed by application ofa film of 53.6percent orthophosphoric acid solution over the same area of the specimenand then again blotted to remove excess liquid. It will be observed thatthe ferrocyanide solution does not produce any color in the treatedfibers even if permitted to remain on the specimen indefinitely.However, a few seconds by orthophosphoric acid, the fibers chemicallytreated with ferric chloride assume a deep blue color. This differentialcolor effect between the chemically treated cellulosic fibers-and theuntreated cellulosic fibers would beimpossible to duplicate withoutstarting at thepoint of the formation of the paper, paperboard or othercellulosic material and then onlywhen the formula and the percentages ofthe various components or of the inorganic chemicals in the treatment ofthe cellulosic fibers and in the testingof the specimen, are known.--

While the invention disclosed herein may be applied to paper, paperboardor other cellulosic materials, it is to be understood that the foregoingdetailed description is merely given by way of illustration and that theinvention is not limited to that material nor. to the exact method orproduction of the paper, paperboard or other cellu-" from. the intent orfrom the spirit of the invention.

Having described our invention it ,is intended that the patent shallcover by suitable expression in the appended claims whateverfeaturesof'patentable novelty exist in 'the invention herein 'disclosed.

We claim: 3

1. The process of manufacturing identifiable paper which comprisesforming an aqueous suspension of cellulosic fibers containing about 1.5percent by weight cellulose, incorporating with said suspension about20,-percent by weight based on cellulosic content, ofhydrated ferricchloride,

hydrolyzing said ferric chloride and precipitating colloidal ferrichydroxide in said fibers by heating said suspension to a temperature orabout 140 degrees F., then incorporating about0.8 percent based on dry.weight of the thus-treated fibers in a paper base stock, and thenforming paper from the resulting mixed stock, whereby the resultingpaper is latently identifiable.

after the application of the orthophosphoric acid solution, the treatedfibers acquire a deep blue color.

' 2. In a process of manufacturing identifiable paper, the steps whichcomprise separately treating about 0.64 percent of the paper stock withIn the present invention it is a unique feature that'treatment of apercentage of the cellulosic fibers tobe incorporated in the feltedfabric ofthe paper, paperboard or other cellulodcmaterial isaccomplished by the fact thatthe ferric chlo-' ride in dilute solutionunder the effect of heat undergoes a hydrolysis to colloidal ferrichydroxide which carrie an electrical charseopposite to about 0.16percent of ferric chloride hexahydrate, hydrolyzingsaid ferric chlorideto-iron hydroxide whereby it is intimately bonded to said paper 1 stock,and then incorporating the thus-treated stock with the remaining 99.2percent of the stock 'and forining paper therefrom.

MORRIS s.

